1. Field of the Invention
The present invention relates to an improvement of a fluid coupling with a baffle plate, comprising a pump impeller connected to an input shaft, a turbine impeller connected to an output shaft disposed coaxially with the input shaft, the pump impeller and the turbine impeller being opposed to each other to define a circulating circuit therebetween, and a baffle plate mounted to at least one of the pump impeller and the turbine impeller to protrude on the side of an inner periphery of the circulating circuit.
2. Description of the Related Art
Such a fluid coupling with the baffle plate is already known.
In such a fluid coupling with the baffle plate, a resistance is provided to the flowing of working oil within the circulating circuit by disposition of the baffle plate, to thereby reduce drag torque. In the known fluid coupling, however, the outside diameter of the baffle plate is set at a large value in order to sufficiently reduce the drag torque, but this configuration provides the following disadvantage: The flowing of working oil within the circulating circuit is obstructed greatly by the baffle plate in a normal rotational speed range, resulting in a large reduction in transmitting efficiency.
Accordingly, it is an object of the present invention to provide a fluid coupling with a baffle plate, wherein a reduction in drag torque and an improvement in transmitting efficiency can be satisfied simultaneously without the above-mentioned disadvantage.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a fluid coupling with a baffle plate, comprising a pump impeller connected to an input shaft, a turbine impeller connected to an output shaft, the pump impeller and the turbine impeller being opposed to each other to define a circulating circuit therebetween, and a baffle plate mounted to at least one of the pump impeller and the turbine impeller to protrude on the side of an inner periphery of the circulating circuit, wherein a, clutch chamber is defined between a back of the turbine impeller and a side cover connected to the pump impeller to cover the back of the turbine impeller, the clutch chamber being divided by a clutch piston into an inner chamber portion on the side of the turbine impeller and an outer chamber portion on the side of the side cover, the clutch piston being axially movably connected to the turbine impeller, thereby constituting a lock-up clutch, so that a first oil passage leading to the outer chamber portion and a second oil passage leading to an inner periphery of the circulating circuit are alternately put into communication with a discharge portion of an oil pump and with an oil reservoir in a switched manner. The input shaft and the output shaft correspond respectively to a crankshaft 1 and a main shaft 2 in embodiments of the present invention, which will be described hereinafter.
With the first feature, during idling or extremely low-speed rotation of the input shaft, the working oil discharged by the oil pump is supplied from the first oil passage to the outer chamber portion and the inner chamber portion of the clutch chamber, and into the circulating circuit, thereby bringing the lock-up clutch into a non-connected state to enable the fluid transmission between the pump impeller and the turbine impeller. At that time, however, a drag torque is reduced since the circulation of the working oil within the circulating circuit is obstructed by the baffle plate, thereby easily maintaining the stopped state of the output shaft.
When the input shaft reaches a predetermined rotational speed or more after starting of the fluid transmission, the working oil discharged by the oil pump is supplied from the second oil passage to the circulating circuit and the inner chamber portion of the clutch chamber, and on the other hand, the outer chamber portion is opened to the oil reservoir through the first oil passage, thereby bringing the lock-up clutch into a connected state to connect the pump impeller and the turbine impeller directly to each other. As a result, it is possible to improve the efficiency of transmission of the rotational torque between the input shaft and the output shaft, irrespective of a reduction in efficiency of transmission of the fluid between the impellers due to the baffle plate.
Therefore, it is possible to satisfy both the reduction in drag torque and the improvement in efficiency of transmission of the fluid between the impellers during normal rotation.
According to a second aspect and feature of the present invention, in addition to the first feature, the pump impeller has a hub disposed to surround a hub of the turbine impeller, and the second oil passage is put into communication with the inner periphery of the circulating circuit through a bearing interposed between the hubs.
With the second feature, an accuracy of concentricity between the pump impeller and the turbine impeller can be secured by the bearing, to ensure a smooth relative rotation between the impellers. Moreover, the working oil flowing into and out of the circulating circuit between the impellers can be passed through the bearing, to lubricate the bearing effectively. Moreover, the working oil flows along the hubs of the pump impeller and the turbine impeller as well as the baffle plate and hence, can cool them effectively. Further, the bearing also serves as a communication passage between the circulating circuit and the second oil passage, which can contribute to simplification of the arrangement of the oil passages.
According to a third aspect and feature of the present invention, in addition to the first or second feature, the baffle plate is connected to the hub of the turbine impeller, and the second oil passage is put into communication with an entrance of the pump impeller within the circulating circuit.
With the third feature, the entrance of the pump impeller, with which the second oil passage communicates, is at a location under a relatively low pressure within the circulating circuit. Therefore, the working oil can be supplied smoothly from the second oil passage to the circulating circuit, to contribute to an improvement in responsiveness to bring the lock-up clutch into a connected state.
According to a fourth aspect and feature of the present invention, in addition to the first or second feature, the baffle plate is connected to the hub of the pump impeller, and the second oil passage is put into communication with an exit of the turbine impeller within the circulating circuit.
With the fourth feature, the exit of the turbine impeller, with which the second oil passage communicates, is at a location under a relatively high pressure within the circulating circuit. Therefore, the flowing of the working oil from the circulating circuit to the second oil passage can be conducted smoothly in the non-connected state of the lock-up clutch, to provide an improvement in responsiveness to bring the lock-up clutch into a non-connected state, and to effectively cool the fluid coupling.
According to a fifth aspect and feature of the present invention, in addition to the fourth feature, the second oil passage is also put into communication with the entrance of the pump impeller within the circulating circuit.
With the fifth feature, the flowing of the working oil from the circulating circuit to the second oil passage can be conducted smoothly in the non-connected state of the lock-up clutch, to effectively cool the fluid coupling. When the working oil is supplied from the second oil passage to the circulating circuit, such supplying can be conducted smoothly, which can contribute to an improvement in responsiveness to bring the lock-up clutch into a connected state.
According to a sixth aspect and feature of the present invention, in addition to the first feature, the pump impeller has a hub disposed to surround a hub of the turbine impeller; a ball bearing is interposed between both the hubs to axially connect the hubs to each other; the circulating circuit and the second oil passage are put into communication with each other through the bearing; and the output shaft is spline-fitted to the hub of the turbine impeller and rotatably fitted to a hub of the side cover.
With the sixth feature, the ball bearing is interposed between the hub of the turbine impeller and the hub of the pump impeller surrounding the hub of the turbine impeller, and the hubs of the impellers are axially connected to each other through the ball bearing. Therefore, an assembly comprising the pump impeller, the turbine impeller and the side cover can be constituted with a highly accurate concentricity provided to the hubs of the pump impeller, the turbine impeller and the side cover. Thus, it is possible to easily conduct the operation of fitting the output shaft to the hubs of the turbine impeller and the side cover. Moreover, the disposition of the hub of the pump impeller to surround the hub of the turbine impeller can contribute to a reduction in axial dimension of the fluid coupling, to increase the degree of freedom of the layout in the vehicle.
Further, the hub of the pump impeller is carried on the hub of the turbine impeller with the ball bearing interposed therebetween and hence, the fitting of the output to the hub of the pump impeller is not required. Thus, it is also possible to remarkably improve the operability of mounting the output shaft.
Yet further, the highly accurate concentricity is provided to the pump impeller and the turbine impeller and hence, the smooth relative rotation between them can be ensured, and the stable coupling function can be exhibited.
In addition, since the circulating circuit and the second oil passage are put into communication with each other through the ball bearing, the working oil flowing into and out of the circulating oil is necessarily passed through the ball bearing and can lubricate the bearing effectively. Moreover, the ball bearing also serves as the communication passage between the circulating circuit and the second oil passage and hence, the arrangement of the oil passages can be simplified, thereby providing a reduction in processing steps and, in turn, a reduction in cost.
According to a seventh aspect and feature of the present invention, in addition to the sixth feature, the ball bearing has an inner race which is fitted over an outer peripheral surface of the hub of the turbine impeller and axially clamped by an annular shoulder of the hub and a stop ring locked to the hub, and an outer race which is fitted to an inner peripheral surface of the hub of the pump impeller and clamped by an annular shoulder of the hub and a stop ring locked to the hub.
With the seventh feature, it is easy to axially connect the ball bearing with the hubs of the pump impeller and the turbine impeller, thereby easily constituting a fluid coupling assembly.